1. Field of the Invention
This invention relates to a color determining device for use in a color printing system, and more particularly to a normalizing circuit used for a color detecting device which detects and determines a particular color in a color original.
2. Description of the Prior Art
It has been proposed in a color printing system to print a particular color in a desirable color when the color original, like a color negative film or a color reversal film, contains a particular color such as flesh color like a human face, hands, legs or any other part of a human body.
In carrying out the above described method, a color determining or detecting device is used for determining if such a particular color exists in the color original, such device being as disclosed in Japanese Patent Publication (first publication) No. 53(1978)-145620.
The color detecting device disclosed therein measures the color components of red, green and blue of scanned points in the color original and normalizes the measured red, green and blue densities by conducting gamma correction and sensitivity correction according to the color original, and then determines if the color consisting of the normalized red, green and blue color components is contained in the region defined by a solid or plane area of the particular color like flesh color.
In the color determining device a normalizing circuit is used to normalize the red, green and blue densities of the point in the color original. The normalizing process is conducted for correcting the gamma value and the sensitivity according to the kind of the color original and the developing condition. In other words, even when the same object is photographed under the same photographing condition, the three color densities on the color original will differ for the different photosensitive materials according to the characteristics of the photosensitive material. Therefore, it is necessary to make the densities of the three colors the same, even for the different photosensitive materials, when the same object is photographed under the same condition. By conducting such normalization, the determination of the color can be accurately made.
The conventional normalizing circuit has a defect in that the addition, subtraction and gain conversion are made by externally turning on and off a switch, and accordingly the operation of the switch for the process is troublesome.